System for charging battery for vehicle

A method for charging a battery via a charging control device having a power factor correction circuit configured to convert an alternating (AC) voltage of a charging apparatus into a direct current (DC) voltage, a DC-DC converter connected to the power factor correction circuit and configured to transform the DC voltage, a capacitor connected to an output terminal of the DC-DC converter, and a relay unit provided between the capacitor and the battery, the method comprising:

• determining, by a control unit connected to the charging control device, a charged state of the capacitor connected between the DC-DC converter and the relay unit, when the charging apparatus is connected to the charging control device,
• determining, by the control unit, whether an initial charging control is required, and
• setting, by the control unit, a maximum frequency and a duty ratio required for pulse width modulation (PWM) control so that the duty ratio is increased, upon concluding that the initial charging control is required, and performing the PWM control on the DC-DC converter in accordance with the maximum frequency and the duty ratio so that a voltage of the charging apparatus is transformed into a capacitor charging voltage for charging the capacitor,
• wherein when the control unit determines that the capacitor voltage is equal to or lower than a reference voltage by directly checking the output voltage of the capacitor, the control unit is configured to conclude that the initial charging control is required, and is configured to perform pulse width modulation (PWM) control on the DC-DC converter in accordance with the initial charging control, and
• wherein upon concluding, by the control unit, that the initial charging control is required, the control unit is configured to set the maximum frequency required for the PWM control and to set the duty ratio for the PWM control so that the duty ratio is gradually increased.